Genistein is a NCI high priority putative prostate cancer (PCa) chemopreventive agent. Our preliminary studies demonstrate that genistein inhibits PCa cell detachment and invasion, which are initial steps in the metastatic cascade. We hypothesize that genistein will also inhibit PCa metastasis by inhibiting the movement of prostate cancer cells from the prostate gland into the circulation in man. In preliminary in vitro studies, we demonstrated that genistein inhibits activation of the pro-cell-motility signaling p38-HSP27 (heat shock protein 27) pathway, while enhancing activation of the anti-motility ALK-2 signaling pathway. In mice, we have shown that genistein inhibits human PCa cell detachment and metastasis. Our first SPORE trial was a phase I clinical trial, and it defined genistein's pharmacology in PCa patients. Our second SPORE trial was a phase 2 pre-prostatectomy design. It demonstrated that (1) genistein was well tolerated, (2) that it inhibited prostate cell detachment, and (3) that it selectively modulated genes that regulate prostate cell motility. In this proposal, we propose three Aims: 1) To determine whether genistein affects motility associated genes and regulatory proteins in human prostate tissue. Using banked prostate tissue from our second SPORE trial, our studies will determine whether genistein alters the function of relevant regulatory pathways in prostate cells. 2) Evaluate in an animal model whether modulation of pro-cell-motility HSP27 has an impact on genistein's ability to inhibit metastases. Human PCa cells engineered to express altered levels of HSP27 will be orthotopically implanted into mice. We will evaluate their ability to form metastasis, with and without genistein treatment. 3) To conduct a Phase II clinical trial to determine whether genistein inhibits movement of PCa cells from the prostate gland into the circulation in high risk pre-prostatectomy patients. We will implement a third SPORE trial to test this hypothesis. Subjects with clinically-localized, high-risk PCa with measurable circulating prostate cells will be accrued on to a prospective phase 2, randomized trial of genistein versus placebo. The resultant effects of genistein on circulating levels of prostate cells will be assessed by a quantitative RT/PCR assay for PSA.